The reproduction metal clips that we have been selling all have different issues. There is at least four different manufactures of the clips and they all have issues. The tangs all seem to be a bit large for the hole diameter. The tempering of the metal also makes them very hard and does not have the "spring like" characteristics of the original clips. Some owners have taken a small file and opened the holes up slightly or remove excess paint buildup common with newer paint jobs. Others have taken a flat file and removed a bit of the material at the tangs.
The plastic style clips did not come about to 1973, but we have not had any issues with them for the guys who have decided to purchase them. The are much cheaper and easier to use and that is the primary reason that guys have gone that route.